1. Field of the Invention
The present invention relates to a valve equipped with a check valve mechanism for preventing backflow of a fluid.
2. Description of the Related Art
In equipment in which a fluid is used, a valve equipped with a check valve mechanism is used to prevent backflow of the fluid. For instance, many of feed water pipings used in water piping systems such as boilers are provided with a valve equipped with a check valve mechanism for preventing backflow of feed water or boiler water. Boiler water has a high pressure and a high temperature, and it is therefore necessary, from the viewpoint of safety and the heatproof temperature of the pre-treatment equipment, that all possible countermeasures be taken against the backflow of the boiler water. To that end, it is necessary to take all possible measures to prevent leakage through the check valve (hereinafter also referred to as “check valve leakage”), that is, to prevent backflow.
As an example of such a valve with a check valve mechanism, there is known one including a check valve mechanism equipped within a valve chamber defined between a fluid inlet and a fluid outlet of a valve casing. The check valve mechanism includes a valve seat having a valve hole formed therein, and a valve body fixed to a valve shaft and arranged on the fluid outlet side of the valve seat, the valve shaft passing through the valve hole of the valve seat and being movably supported on the fluid inlet and outlet sides of the valve seat; when applied with a fluid pressure acting in the direction from the fluid inlet side to the fluid outlet side, the valve body moves away from the valve seat to thereby open the valve hole, and when applied with a fluid pressure acting in the direction from the fluid outlet side to the fluid inlet side, the valve body moves toward and into abutment with the valve seat, thus closing the valve hole (for example, see JP 07-101066 B).
With the valve equipped with a check valve mechanism as disclosed in JP 07-101066 B mentioned above, however, clogging of refuse between the valve seat and the valve body, deformation of the valve body, or the like may impair the sealing property of the check valve mechanism, leading to check valve leakage, that is, occurrence of fluid backflow. In view of this, as a measure for preventing fluid backflow, a construction has been employed in which a plurality of valves with a check valve mechanism are connected in series in the piping. However, this construction, in which a plurality of valves with a check valve mechanism are connected in series in the piping, results in increased piping length and an increase in the space required for accommodating such enlarged piping, and also requires rather complicated connection arrangement, leading to an inevitable increase in cost.